Larger doses of STS are required to induce vasospasm in older patients, males, and those with larger veins. Regardless of gender and age, larger veins are more likely to recanalize, but are not necessarily associated with clinical recurrence. Although older patients and males tend to have larger veins, their recanalization rates are similar to younger patients and females when sufficiently higher STS doses are used to induce vasospasm. Ambulatory patients of all ages and either gender may be good candidates for UGS if vasospasm is used as the treatment endpoint. Contrary to prevailing opinion, large vein caliber is not an absolute contraindication for UGS.